In the first statewide primary election since the Top Two Candidates Open Primary Act took effect January 1, 2011, Californians will weigh in on 155 state legislative and congressional contests. The new open primary law requires that all candidates for a voter-nominated office (previously known as a partisan office) be listed on the same ballot. Anyone can vote for any candidate for the office, regardless of party preference, then only the two candidates receiving the most votes move on to the November 6 General Election. The top two voter-getters move on to the general election regardless of vote totals; even if there are only two candidates in the open primary, a general election is still required.

The Top Two Candidates Open Primary Act does not apply to candidates running for U.S. president, county central committee and local offices. Voters who indicated a political party preference on their voter registration forms may only vote for a presidential candidate in the primary election of their preferred party. While the Americans Elect Party has chosen not to participate in California’s Presidential Primary Election, the other qualified political parties are holding their presidential primaries in one of two ways:

Closed presidential primary, in which only voters indicating a preference for the party may vote for that party's presidential nominee. The Republican, Green, Libertarian, and Peace and Freedom parties are holding closed presidential primaries on June 5.

Modified-closed primary, in which the party also allows voters who registered with no party preference (NPP voters – previously known as decline-to-state voters) to vote for that party's presidential nominee. The American Independent and Democratic parties are allowing NPP voters to vote their June 5 presidential primary ballot. (A voter may not request more than one party's presidential ballot.)

The first June 5 primary election ballots may go out to California's military and overseas voters as early as April 6. The last day to register to vote in the June 5 primary election is May 21. The last day to request a vote-by-mail ballot is May 29.

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